PHP Server Side Scripting Forum

Which is the best php driven open source Discussion Forum script? I have alreay tried PHPBB. Is there any other better and customizable Open source PHP forum that can easily handle large number of users at a time say 500 users?

i would be glad to know either. i know some people who have phpbb run on 500+ users and it did the job but i do not have much to compare. phorum states that it can do the job but i have no experiences with phorum. anyone has?

Well it would also depend greatly on the hardware running the site. Phpbb is extremely fast and capable of handing those numbers expecially if you remove as much of the dynamic fluff as you can i.e whos online, lastest post etc etc.